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In this work, MnCoNiO x (denoted as MCNO) nanocrystals (with a size of less than 30 nm) finely encapsulated in double-carbon (DC, including reduced graphene oxide and amorphous carbon derived by polymer) composite nanofibers (MCNO@DC) were successfully synthesized via an electrospinning method followed by a sintering treatment. The as-obtained MCNO@DC nanofibers present superior sodium storage performance and retain an especially high specific capacity of 230 mAh g -1 with a large capacity retention of about 96% at 0.1 A g -1 after 500 cycles and a specific capacity of 107 mAh g -1 with capacity retention of about 89% at 1 A g -1 after 6500 cycles. The outstanding cycle characteristic is mainly due to the tiny MCNO nanoparticles, which shorten the ion migration distance, and the three-dimensional DC framework, which remarkably promotes the electronic transfer and efficiently limits the volume expansion during the progress of insertion and extraction of Na + ions. Moreover, nitrogen doped in carbon is able to improve the electrochemical capability as well. Finally, kinetic analysis of the redox reactions is used to verify the pseudocapacitive mechanism in charge storage and the feasibility of using MCNO@DC composite nanofibers as an anode for sodium-ion batteries with the above-mentioned behavior.

Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100,000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process.

All-solid-state microsupercapacitors (MSCs) have been receiving intense interest due to their potential as micro/nanoscale energy storage devices, but their low energy density has limited practical applications. It has been reported that gel electrolytes based on ionic liquids (ionogels) with large potential windows can be used as solid electrolytes to enhance the energy density of MSCs, but a systematic study on how to select and evaluate such ionogels for MSCs is rare. In this study, we construct a series of all-solid-state asymmetric MSCs on the interdigital finger electrodes, using graphene quantum dots (GQDs) as the negative electrode, MnO2 nanosheets as the positive electrode, and different ionogels as the solid electrolytes. Among them, the MSC using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTF2]) with 4 wt % fumed SiO2 ionogel exhibited the best electrochemical performance, having excellent rate capability with the scan rate up to 2000 V s(-1), ultrafast frequency response (τ0 = 206.9 μs) and high energy density. The outstanding performance of this device mainly results from fast ion diffusion, high ion conductivity of the ionogel, and ionic liquid-matrix interactions. The results presented here provide guidance for picking out appropriate ionogels for use in high-performance all-solid-state MSCs to meet the growing requirement of micronanoscale energy storage devices. Additionally, the ultrafast frequency response of our MSCs suggests potential applications in ac line-filters.

Business costs and energy/environmental concerns have increased interested in biomass materials for production of activated carbons, especially as electrode materials for supercapacitors or as solid-state adsorbents in CO₂ adsorption area. In this paper, waste celtuce leaves were used to prepare porous carbon by air-drying, pyrolysis at 600 °C in argon, followed by KOH activation. The as-prepared porous carbon have a very high specific surface area of 3404 m²/g and a large pore volume of 1.88 cm³/g. As an electroactive material, the porous carbon exhibits good capacitive performance in KOH aqueous electrolyte, with the specific capacitances of 421 and 273 F/g in three and two-electrode systems, respectively. As a solid-state adsorbent, the porous carbon has an excellent CO₂ adsorption capacity at ambient pressures of up to 6.04 and 4.36 mmol/g at 0 and 25 °C, respectively. With simple production process, excellent recyclability and regeneration stability, the porous carbon that was derived from celtuce leaves is among the most promising materials for high-performance supercapacitors and CO₂ capture.